A bis(pyrazolylpyridyl) ligand, L, containing a central photochromic dithienylethene spacer predictably forms a ferrous [Fe L ] helicate exhibiting spin crossover (SCO). In solution, the compound [Fe L ](ClO ) (1) preserves the magnetic properties and is fluorescent. The structure of 1 is photo-switchable following the reversible ring closure/opening of the central dithienylethene via irradiation with UV/visible light. This photoisomerization switches on and off some emission bands of 1 and provides a means of externally manipulating the magnetic properties of the assembly.
Controlling the charges and spins of molecules lies at the heart of spintronics. A photoswitchable molecule consisting of two independent spins separated by a photoswitchable moiety was designed in the form of new ligand H L, which features a dithienylethene photochromic unit and two lateral coordinating moieties, and yields molecules with [MM⋅⋅⋅MM] topology. Compounds [M L (py) ] (M=Cu, 1; Co, 2; Ni, 3; Zn, 4) were prepared and studied by single-crystal X-ray diffraction (SCXRD). Different metal centers can be selectively distributed among the two chemically distinct sites of the ligand, and this enables the preparation of many double-spin systems. Heterometallic [MM'⋅⋅⋅M'M] analogues with formulas [Cu Ni L (py) ] (5), [Co Ni L (py) ] (6), [Co Cu L (py) ] (7), [Cu Zn L (py) ] (8), and [Ni Zn L (py) ] (9) were prepared and analyzed by SCXRD. Their composition was established unambiguously. All complexes exhibit two weakly interacting [MM'] moieties, some of which embody two-level quantum systems. Compounds 5 and 8 each exhibit a pair of weakly coupled S=1/2 spins that show quantum coherence in pulsed Q-band EPR spectroscopy, as required for quantum computing, with good phase memory times (T =3.59 and 6.03 μs at 7 K). Reversible photoswitching of all the molecules was confirmed in solution. DFT calculations on 5 indicate that the interaction between the two spins of the molecule can be switched on and off on photocyclization.
One of the benefits found in crystal engineering to built molecular materials is the possibility of understanding, and thus finely controlling their photochromic performance in the solid state. We have discovered potential hints in this direction through the use of the photochromic ligand 1,2-bis(5-carboxy-2-methylthien-3-yl)cyclopentene, H2L, in reactions with either of two Cu(II) salts for the formation of two new solvatomorphs of a coordination polymer, [Cu(L)(py)3]•2py (1a) and [Cu(L)(py)3]•2H2O•0.5Et2O (1b). H2L is a diarylethene ligand that exhibits reversible photocyclization, potentially allowing to reversibly modifying the exchange coupling between paramagnetic species separated by such moiety. While the backbone of both compounds is the same, their supramolecular organization significantly differs, leading to different photochromic properties, in particular regarding the reversibility of their photoswitching processes. These remarkable structure/property relations have been assessed by optical reflectivity and Raman measurements, in light of the respective crystallographic structures.
In the presence of Na(+) ions, the reaction of the ligand 2-hydroxy-1,3-bis-(3-oxo-3-(2-hydroxyphenyl)-propionyl)-benzene, H5L4, with M(AcO)2 salts (M = Mn, Co) gathers the conditions for the assembly of coordination complexes (NBu4)3[M2Na2(H2L4)3] (M = Mn(II) 1 and Co(II) 2), which exhibit a new paddle-wheel structure. The features of this new category of compounds are discussed as well as their magnetic properties and solution behaviour.
A bis(pyrazolylpyridyl) ligand, L, containing a central photochromic dithienylethene spacer predictably forms a ferrous [Fe2L3]4+ helicate exhibiting spin crossover (SCO). In solution, the compound [Fe2L3](ClO4)4 (1) preserves the magnetic properties and is fluorescent. The structure of 1 is photo‐switchable following the reversible ring closure/opening of the central dithienylethene via irradiation with UV/visible light. This photoisomerization switches on and off some emission bands of 1 and provides a means of externally manipulating the magnetic properties of the assembly.
The synthesis of molecular cluster pairs is a challenge for coordination chemists due to the potential applications of these species in molecular spintronics or quantum computing. The ligand H(4)L, 1,3-bis-(3-oxo-3-(2-hydroxyphenyl)-propionyl)-2-methoxybenzene, has been successfully used to obtain a series of such complexes using the basic Fe(III) trinuclear carboxylates as starting materials. Synthetic control has allowed the isolation of the two molecular cluster pairs that form the composite [Fe(4)O(2)(PhCO(2))(6)(H(2)L)(pz)](2)[Fe(3)O(PhCO(2))(5)(py)(H(2)L)](2) (1). The dimers of trinuclear units, [Fe(3)O(PhCO(2))(5)(H(2)O)(H(2)L)](2) (2) and [Fe(3)O(o-MePhCO(2))(5)(H(2)L)(py)](2) (3), and the dimers of tetranuclear units, [Fe(4)O(2)(PhCO(2))(6)(H(2)L)(pz)](2) (4) and [Fe(4)O(2)(o-MePhCO(2))(6)(H(2)L)(pz)](2) (5), are presented here. The magnetic properties of the reported aggregates show that they are pairs of semi-independent clusters weakly interacting magnetically as required for two-qubit quantum gates.
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